Wireless LANs (Local Area Networks) defined in, for example, the IEEE (The Institute of Electrical and Electronics Engineers, Inc.) 802.11 (for example, IEEE802.11a or IEEE802.11b) communication standard have been known for wireless communication for realizing high-speed data transmission.
Nowadays, with the increasing functionality of digital equipment, digital equipment including wireless communication devices that can use wireless LANs has been in widespread use. Digital equipment can transmit a large amount of data (for example, HD (High-Definition) video data) to other digital equipment, for example, by causing wireless communication devices to directly communicate with each other without the involvement of an access point.
As a communication method for causing wireless communication devices to directly communicate with each other, for example, wireless communication using 60 [GHz] millimeter waves has attracted attention. Millimeter wave communication uses a broader band than conventional wireless LAN communication and thus enables high-speed wireless communications, for example, at 1 [Gbps] or higher, when a range where millimeter wave communication is allowed is effectively utilized. However, radio waves in the 60 [GHz] millimeter wave band have short wavelengths and have a strong characteristic of traveling straight, and are thus susceptible to changes in a radio-wave propagation environment (in the communication environment).
For example, when a human crosses or an obstruction exists between a wireless communication device that transmits data and a wireless communication device that receives the data or when the hand of a human who holds either of the wireless communication devices moves or rotates, the communication environment changes, and the quality of communication deteriorates. Hereinafter, a wireless communication device that transmits data is referred to as a “data-transmitting wireless communication device”, and a wireless communication device that receives data is referred to as a “data-receiving wireless communication device”. Also, the data-transmitting wireless communication device has a configuration including a wireless transmitting unit and a wireless receiving unit, and the data-receiving wireless communication device has a configuration including a wireless transmitting unit and a wireless receiving unit.
Accordingly, in millimeter wave communication, beamforming is used to set, for example, a beam pattern that suits one of the directivities of a transmitting antenna and a receiving antenna or a beam pattern that suits both of the directivities of the transmitting antenna and the receiving antenna. The beam pattern of each antenna is set for a single communication partner or is set so that it is appropriate for a plurality of communication partners, although this is not optimum.
In wireless communication devices that use the millimeter wave band to perform wireless communication, the transmitting antenna and the receiving antenna may be used separately, taking the amount of signal attenuation into account, and different beam patterns may be set for the transmitting antenna and the receiving antenna. For example, the receiving antenna is set to be omnidirectional, and a beam pattern having a main beam formed in a particular direction is set for the transmitting antenna.
Also, communication protocols in millimeter wave communication involve a process (a procedure) for determining the beam pattern of the transmitting antenna or the receiving antenna. For example, Patent Literature 1 is known as prior art for determining the beam pattern of an antenna in millimeter wave communication.
In Patent Literature 1, each time a data-transmitting wireless communication device transmits a transmission frame, it starts a timer and counts the number of transmissions (the number of retransmissions) of a transmission frame (a data frame). When the data-transmitting wireless communication device retransmits a data frame because a response with an Ack frame is not returned from a data-receiving wireless communication device, the data-transmitting wireless communication device changes the beam pattern of the transmitting antenna to another beam pattern, when the count value of the timer or the number of retransmissions of the transmission frame reaches a certain value.